New Memristor Circuit Mimicks Synapses in the Brain

Illustration: University of Massachusetts, Amherst

To a human brain, picking one particular image out of a thousand is an easy task. Billions of neurons and the synapses that connect them can quickly process information in parallel to make a decision. Seeking to make such processing that easy for machines, scientists and engineers have been working with devices called memristors, which have some similar behaviors to neural synapses. Engineers at the University of Massachusetts report this week that they’ve invented a memristor circuit that matches a synapses’ behavior more closely than any before.

First predicted in 1971 and invented in 2008 by HP, memristors are so named because they remember how much voltage you applied across the device and how long you applied it, storing the information as a change in resistance. HP engineers noticed immediately that such a characteristic was similar to the way the synaptic connection between neurons strengthens with use to form a memory.

Memristors are “kind of the ideal candidate in many aspect” says Jianhua Yang, an electrical engineer at the University of Massachusetts Amherst working on improving their behavior. Low-power, simple circuits of memristors could improve the ability of computers to solve power-intensive computer vision and machine learning tasks that human brains handle with little effort.

In research published in Nature Materials on 26 September, Yang and his team mimicked a crucial underlying component of how synaptic connections get stronger or weaker: the flow of calcium.

The movement of calcium into or out of the neuronal membrane, neuroscientists have found, directly affects the connection. Chemical processes move the calcium in and out— triggering a long-term change in the synapses’ strength. 2015 research in ACS NanoLetters and Advanced Functional Materials discovered that types of memristors can simulate some of the calcium behavior, but not all.

In the new research, Yang combined two types of memristors in series to create an artificial synapse. The hybrid device more closely mimics biological synapse behavior—the calcium flow in particular, Yang says.

The new memristor used--called a diffusive memristor because atoms in the resistive material move even without an applied voltage when the device is in the high resistance state—was a dialectric film sandwiched between Pt or Au electrodes. The film contained Ag nanoparticles, which would play the role of calcium in the experiments.

By tracking the movement of the silver nanoparticles inside the diffusive memristor, the researchers noticed a striking similarity to how calcium functions in biological systems.

A voltage pulse to the hybrid device drove silver into the gap between the diffusive memristor’s two electrodes–creating a filament bridge. After the pulse died away, the filament started to break and the silver moved back— resistance increased.

Like the case with calcium, a force made silver go in and a force made silver go out.

To complete the artificial synapse, the researchers connected the diffusive memristor in series to another type of memristor that had been studied before.

When presented with a sequence of voltage pulses with particular timing, the artificial synapse showed the kind of long-term strengthening behavior a real synapse would, according to the researchers. “We think it is sort of a real emulation, rather than simulation because they have the physical similarity,” Yang says.

He says the next step is to better understand the mechanisms. Then, his team plans to combine the artificial synapses into arrays and eventually build bio-inspired circuits.

“We can have a more direct, more natural, and a more complete emulation to the synaptic system using the silver-based system,” he says.

ORIGINAL: IEEE Spectrum

By Andrew Silver

Posted 29 Sep 2016

How Would Nature Create A ‘Generous City’?

ORIGINAL: Triple Pundit
By Tamsin Woolley-Barker, Ph.D
By 3p Contributor | July 9th, 2013

Project Haiti Aerial – Credit – HOK by HOK Network, on Flickr

At the end of June, over 350 bio-inspired teachers, designers, architects, biologists, industrialists, and policy-makers gathered at the University of Massachusetts in Boston to ask, “How can humans create conditions conducive to Life?” Not just sustainable economies, cities, and production systems, but a regenerative way of life that creates biodiversity instead of destroying it.

At the 7th Annual Biomimicry Education Summit, and the first ever Biomimicry 3.8 Global Conference, a heady mix of dreamers and doers were trying to build our future the way nature would do it.

On the conference’s second day, a panel of notable architects and city planners asked “How would nature design buildings and cities that fulfill the ecosystem services of the original habitats they replaced?” This is the promise of “Generous Cities,” places where our buildings actually regenerate and improve our environment, much like other richly productive ecosystems we find in nature. Complex living systems like coral reefs and rain forests have been around for millions of years, shaped by natural selection into collaborative webs that are much more than the sum of their parts. Thomas Knittel of HOK and Chris Garvin of Terrapin Bright Green spoke of the need to engineer analogous ecosystems in our urban cores.

In New York, this vision is actually beginning to guide urban planning and architecture, thanks to the Wildlife Conservation Society’s ambitious Mannahatta Project, which reconstructed Manhattan’s environment at the time of European arrival. We now know that the biodiversity per acre on the island once rivaled that of national parks like Yellowstone, Yosemite and the Great Smoky Mountains, with over 55 ecological communities, including forests, meadows, freshwater wetlands, salt marshes, beaches, springs, ponds, and streams, and a rich and abundant community of wildlife.

Knittel spoke of his early training as an architect. Building designers, he said, are taught to get water “off the building, away from it, and keep away.” Everything outside a five foot radius “is a civil engineer’s problem.” Instead, he suggested we look at the way nature manages resources. Nature’s way with water, for instance, is to “slow it, sink it, store it.” In the Amazon rain forest, clouds form in the dry season, despite the shallow soils and lack of rain. Scientists have long asked, “Where does the water come from?” It turns out that some keystone tree species sink and store water in deep taproots. When conditions are dry, the water draws up passively, through transpiration, to the benefit of all species in the ecosystem. Knittel asked whether someday we could “design a building that creates a raincloud?”

Similarly, can our cities become carbon sinks, absorbing atmospheric carbon dioxide the way coral reefs do? Can they run on energy from the sun, wind, water, and heat of the earth, like rain forests and deep-water thermal vent communities? Can our buildings provide food and habitat for ourselves and other species (and not just cockroaches, pigeons, and rats)?

It’s an inspirational vision, and one whose time has come. The Bank of America building, for instance, emits air three times cleaner than the air it brings in. The newly planned Google building, also in NYC, will tap an underground stream for its water needs, while producing a surplus of energy to be fed into the city electricity grid. Green roofs will absorb water and carbon dioxide, while cooling the air.

Thad Pawlowski, an urban designer at New York City Department of City Planning Urban Design Division, then described New York City’s urgent search for ways to rebuild for resilience in the wake of Hurricane Sandy. New flood maps show that the city is dramatically more vulnerable than previously thought, and city planners know that flooding can and will get much worse. Suggestions have mostly been along the lines of “build walls to keep water out.” But nature doesn’t generally rely on such energetically and materially expensive solutions. How would nature rebuild?

Hurricane Sandy damaged Cape May National Wildlife Refuge (NJ) by U. S. Fish and Wildlife Service – Northeast Region, on Flickr

Janine Benyus, Biomimicry 3.8 co-founder and author of the book Biomimicry, which launched the movement and gave it a name, took the mic and spoke with eloquence. “If you want to know how to rebuild,” she said, “Go to the shoreline. Ask what survived there, and why. Look for the survivors and replicate their strategies.” She painted a compelling image of humble grasses rebuilding dunes, and oyster beds acting as reefs, sheltering the land from impact.